Closed cyclone FCC catalyst separation method and apparatus

ABSTRACT

Disclosed is a method and apparatus for fluid catalytic cracking (FCC). The output of a reactor riser zone is fed to a riser cyclone separator, a primary cyclone separator, and secondary cyclone separators, connected in series within a single reactor vessel. The riser cyclone separator is connected to the primary cyclone separator by a conduit, which prevents random post-riser thermal cracking of the hydrocarbons after they exit the riser cyclone separator. The conduit contains an annular port to allow stripping gas to enter the conduit to improve the separation of hydrocarbons from catalyst. Catalyst separated in the riser cyclone separator drops through a riser cyclone dipleg and passes through a dipleg seal which comprises a seal pot or catalyst held around the dipleg. The conduit is formed by two overlapping parts, one having a larger diameter than the other to form the annular port and packing or spacers may be used to align and space the overlapping parts.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method and apparatus for the separation of acatalyst phase from a gas suspension phase in a fluidized catalyticcracking unit (FCC). More particularly, it relates to an improved methodand apparatus for separating the catalyst phase from the gas suspensionphase, as the gas suspension phase is discharged from a riser conversionzone outlet, to minimize or substantially eliminate post-riserconversion zone cracking.

2. Discussion of the Prior Art

The field of catalytic cracking, particularly fluid catalytic cracking,has undergone significant development improvements due primarily toadvances in catalyst technology and product distribution obtainedtherefrom. With the advent of high activity catalysts and particularlycrystalline zeolite cracking catalysts, new areas of operatingtechnology have been encountered requiring refinements in processingtechniques to take advantage of the high catalyst activity, selectivityand operating sensitivity.

By way of background, the hydrocarbon conversion catalyst usuallyemployed in an FCC installation is preferably a high activitycrystalline zeolite catalyst of a fluidizable particle size. Thecatalyst is transferred in suspended or dispersed phase conditiongenerally upwardly through one or more riser conversion zones (FCCcracking zones) providing a hydrocarbon residence time in eachconversion zone in the range of 0.5 to about 10 seconds, and usuallyless than about 8 seconds. High temperature riser hydrocarbonconversions, occurring at temperatures of least 1000° F. or higher andat 0.5 to 4 seconds hydrocarbon residence time in contact with thecatalyst in the riser, are desirable for some operations beforeinitiating separation of vaporous hydrocarbon product materials from thecatalyst. Rapid separation of catalyst from hydrocarbons discharged froma riser conversion zone is particularly desirable for restrictinghydrocarbon conversion time. During the hydrocarbon conversion step,carbonaceous deposits accumulate on the catalyst particles and theparticles entrain hydrocarbon vapors upon removal from the hydrocarbonconversion step. The entrained hydrocarbons are subjected to furthercontact with the catalyst until they are removed from the catalyst bymechanical means and/or stripping gas in a separate catalyst strippingzone. Hydrocarbon conversion products separated from the catalyst andstripped materials are combined and passed to a product fractionationstep. Stripped catalyst containing deactivating amounts of carbonaceousmaterial, hereinafter referred to as coke, is then passed to a catalystregeneration operation.

Of particular interest has been the development of methods and systemsfor separating catalyst particles from a gas suspension phase containingcatalyst particles and vaporous hydrocarbon product materials,particularly the separation of high activity crystalline zeolitecracking catalysts, under more efficient separating conditions so as toreduce overcracking of hydrocarbon conversion products and promote therecovery of desired products of a hydrocarbon conversion operation.Cyclonic equipment is now typically used for efficient separation offluidizable catalyst particles from the gas suspension phase. However,present day cyclonic equipment often permits an undesirable extendedresidence time of the product vapor within a large reactor vessel. Thisextended residence time reduces the desired product yield by as much as4 percent through non-selective thermal cracking. Recent developments inthis art have been concerned with the rapid separation and recovery ofentrained catalyst particles from the gas suspension phase.

Various processes and mechanical means have been employed heretofore toeffect rapid separation of the catalyst phase from the hydrocarbon phaseat the termination of the riser cracking zone, to minimize contact timeof the catalyst with cracked hydrocarbons. Several of these arediscussed below.

Cartmell, U.S. Pat. No. 3,661,799, discloses a process for catalyticconversion of petroleum feedstocks wherein the fluidized mixture of thecracking catalyst and cracked feedstock leaves a vertically-disposedreactor section and enters a cyclone separator, placed in a separatestripper vessel, through a conduit. The conduit contains an annuluswhich allows an inert stripping gas and associated stripped vapors topass into the cyclone separator.

Anderson et al., U.S. Pat. No. 4,043,899, discloses a method for rapidseparation of a product suspension, comprising fluidized catalystparticles and the vaporous hydrocarbon product phase, by discharging theentire suspension directly from the riser conversion zone into a cycloneseparation zone. The cyclone is modified to include a separate cyclonicstripping of the catalyst separated from the hydrocarbon vapors. In themethod of Anderson et al., the cyclone separator is modified to includean additional downwardly extending section comprising a lower cyclonestage. In this arrangement, catalyst separated from the gasiformmaterial in the upper stage, slides along a downwardly sloping baffle tothe lower cyclone where stripping steam is introduced to furtherseparate entrained hydrocarbon products from the catalyst recovered fromthe upper cyclone. The steam and the stripped hydrocarbons are passedfrom the lower cyclone through a concentric pipe where they are combinedwith the hydrocarbon vapors separated in the upper cyclone. Theseparated and stripped catalyst is collected and passes from the cycloneseparator by conventional means through a dipleg. This process requiresthat the entire volume of catalyst, gasiform phase and stripping steampass through the cyclone separator, which means that this equipment mustbe designed to efficiently handle not only a large vapor volume, butalso a large quantity of solid particles.

Myers et al., U.S. Pat. No. 4,070,159, provides a separation meanswhereby the bulk of catalyst solids is discharged directly into asettling chamber without passing through a cyclone separator. In thisapparatus, the discharge end of the riser conversion zone is in opencommunication with the disengaging chamber such that the catalystdischarges from the riser in a vertical direction into the disengagingchamber which is otherwise essentially closed to the flow of gases. Thecyclone separation system is in open communication with the riserconversion zone by means of a port located upstream from, but near, thedischarge end of the riser conversion zone. A deflector cone mounteddirectly above the terminus of the riser causes the catalyst to bedirected in a downward path so as to prevent the catalyst from abradingthe upper end of the disengaging vessel. The cyclone separator is of theusual configuration employed in a catalytic cracking unit to separateentrained catalyst particles from the cracked hydrocarbon products sothat the catalyst passes through the dipleg of the cyclone to the bodyof the catalyst in the lower section of the disengaging vessel, and thevaporous phase is directed from this vessel to a conventionalfractionation unit. There is essentially no net flow of gases within thedisengaging vessel beyond that resulting from a moderate amount of steamintroduced to strip the catalyst residing in the bottom of thedisengaging vessel.

Haddad et al., U.S. Pat. No. 4,219,407, discloses the separation of thecatalyst from the gasiform cracked products in a fashion which permitseffective steam stripping of the catalyst. The suspension of catalystand gasiform material is discharged from the riser conversion zoneoutwardly through radially extending passageways, or arms, whichterminate in a downward direction. Catalyst stripping zones, orstrippers, are located beneath the terminus of each of the radiallyexending passageways. Each stripper consists of a vertical chamber openat the top and the bottom with downwardly sloping baffles located withinthe chamber so as to cause the catalyst to flow in a discontinuousmanner countercurrently to upwardly flowing stripping steam introducedat the lower end of the stripping chamber. The radially extending armsare each provided with a curved inner surface and confining sidewalls toimpart a cyclonic concentration of catalyst particles promoting a forcedseparation thereof from the hydrocarbon vapors. The separation of thecatalyst from the vapors is basically achieved through rapid changes inthe direction of flow of the catalyst and the vapors. Thus the cycloniccollection and concentration of catalyst particles is used to reversethe flow of separated catalyst such that it concentrates as a downwardlyconfined stream which discharges generally downwardly and into the openupper end of the catalyst stripping chamber. A vapor disengaging spaceis provided between the discharge end of the radially extending arms andthe top of the catalyst strippers to promote the rapid removal ofseparated vapors form the catalyst. The separated vapors pass upwardlythrough the disengaging vessel to the open inlet of a cyclone separatorwhich removes entrained catalyst from the gasiform material for returnthrough a dipleg to the body of steam stripped catalyst while theseparated vaporous material passes to a fractionation unit. Thehydrocarbon product, as it passes within the disengaging vessel from thedischarge of the radially extending arms to the cyclone separator,travels in a random fashion and is exposed to catalytic reactiontemperatures which may cause undesirable side reactions and thermalcracking before these vapors enter a quench zone in the mainfractionator of the fluid cracking unit.

Haddad et al., in U.S. patent application, Ser. No. 400,843, filed July22, 1982, the disclosure of which is incorporated herein by reference,disclose an FCC reactor comprising a riser with radially extendingsidearms as the first catalyst-hydrocarbon separation means. Thesidearms force the suspension of the catalyst and the hydrocarbons tosuddenly change the direction of flow from the vertical to thehorizontal thereby forcing preliminary separation of the gaseoushydrocarbons from the solid catalyst particles. The catalyst particlesfall in a downward direction, to a stripping means, while thehydrocarbons, with some entrained catalyst particles, proceed to asecondary separation means, such as a cyclone. The sidearms and thesecondary separation means are enclosed by a vertical conduit to preventrandom uncontrolled thermal cracking of the hydrocarbons. However, thevertical conduit provided to send hydrocarbons from the side arms to thesecondary separation means does not accommodate radial and longitudinalthermal expansion of the separation means.

SUMMARY OF THE INVENTION

It is a primary object of this invention to provide an improved processand apparatus for rapidly separating cracking catalyst from ahydrocarbon vapor/catalyst particle suspension in a fluid catalyticcracking (FCC) process.

It is another object of this invention to provide a method and anapparatus for separating cracking catalyst from hydrocarbonvapor/catalyst suspension, whereby the length of time the suspension issubjected to high temperature after separation from the bulk of thecatalyst is minimized so as to reduce overcracking of the crackedproducts.

It is another object of this invention to provide an apparatus foradmitting a stripping gas to a hydrocarbon vapor/catalyst particlesuspension, wherein a conduit between first and second catalystseparating cyclones has an annular port therein for admitting thestripping gas to the suspension.

It is another object of this invention to provide an apparatus forsealing the bottom opening of a cyclone dipleg by holding a bed ofcatalyst around the dipleg opening, while allowing catalyst to flow outof the dipleg.

It is another object of this invention to provide a method for fluidcatalytic cracking in which a hydrocarbon vapor/catalyst particlesuspension passes directly from a riser into a series of cyclonicseparators, which separate the catalyst particles from the suspensionand which add stripping gas to the suspension as it passes from onecyclonic separator to the next.

It is another object of this invention to provide a cyclonic separationapparatus which better withstands thermal expansion.

It is another object of this invention to provide a method and apparatusfor aligning concentric conduits passing a hydrocarbon vapor/catalystparticle suspension so that they better withstand thermal expansion.

It is another object of this invention to provide an improved method forconverting an open cyclone FCC system to a closed cyclone FCC systemwhich requires a minimum of expense and downtime.

In its method aspects, the invention achieves the foregoing objects byan FCC method comprising the steps of passing a suspension of catalystand hydrocarbon vapors through an FCC cracking zone, such as an FCCriser, passing the cracked hydrocarbons through a first enclosed conduitinto a riser (first) cyclone which separates catalyst from thesuspension, further passing the suspension from the first cyclone to asecond cyclone through a second conduit comprising a gas tube and aninlet duct to the second cyclone, the inlet duct having a largerdiameter than the gas tube, thus forming a first annular port andpassing a stripping gas from a reactor vessel through the annular portto form a mixture with the cracked hydrocarbon vapor/catalyst particlesuspension.

The method may also include the steps of passing the suspension throughsubsequent cyclones and finally to a fractionation zone. In the methodof the invention, separated catalyst passes through cyclone diplegs to acatalyst stripping zone. Since the pressure inside the riser cyclone isslightly higher than the pressure in the reactor vessel, the catalystpasses through a riser cyclone dipleg sealing means before entering thecatalyst stripping zone.

In its apparatus respects, the invention comprises: a reactor vesselhousing a riser hydrocarbon conversion zone, which is an elongatedtubular conduit having a downstream end which terminates in the reactorvessel; means for feeding a suspension of hydrocarbon and catalyst intothe riser conversion zone to produce a mixture of catalyst and crackedhydrocarbon, which exits from the downstream end of the riser conversionzone; a riser (first) cyclone connected to a downstream end of saidriser conversion zone by a first enclosed conduit, a primary (second)cyclone connected to an outlet of the riser cyclone by a second conduit,which comprises a gas tube and an inlet duct to the primary cyclone,which has a larger diameter than the gas tube to form an annular portbetween them, the first conduit completely separating the suspensionpassing therethrough from the atmosphere of the reactor vessel. Theapparatus of the invention may also include means for conducting crackedhydrocarbons from the primary cyclone and reactor vessel out of thereactor vessel. A catalyst stripping zone is also located within thereactor vessel and dipleg means are provided for conducting catalystfrom the cyclones to the catalyst stripping zone. The annular portallows at least a portion of a stripping gas from the catalyst strippingzone to pass directly into the second conduit means. Packings and/orspacers may also be provided for aligning the gas tube and inlet duct. Aseal for the riser cyclone is preferably provided by surrounding abottom opening of the cyclone dipleg with a bed of catalyst, whileallowing catalyst to flow out of the dipleg and through the sealingmeans.

The invention, in both its method and apparatus aspects, can beconfigured as an original installation, or as a retrofit to an existingopen cyclone FCC reactor system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a side view of a fluid catalyticcracking (FCC) reactor of the prior art;

FIG. 2 is a schematic representation of a side view of a fluid catalyticcracking (FCC) reactor of one embodiment of the present invention;

FIG. 3 is a schematic representation of a side view of a fluid catalyticcracking (FCC) reactor of another embodiment of the present invention;

FIG. 4 is an illustration of the detail of the conduit between the risercyclone and the primary cyclone;

FIG. 5 is an illustration of the detail of a section 5--5 in FIG. 4;

FIG. 6 is an enlarged sectional view of the seal pot shown in FIG. 3;

FIG. 7 is an enlarged side sectional view of the conduit between theriser cyclone and primary cyclone showing a packing used to space andalign concentric conduit portions;

FIG. 7A is a top plan view of the FIG. 7A conduit;

FIG. 8 is an enlarged side sectional view of the conduit between theriser cyclone and primary cyclone showing mechanical spacers used tospace and align concentric conduit portions; and

FIG. 8A is a top plan view of the FIG. 8 conduit.

DETAILED DESCRIPTION OF THE INVENTION

As well known, a fluid catalytic cracking (FCC) process employs acatalyst in the form of very fine particles which act as a fluid whenaerated with a vapor. The fluidized catalyst is circulated continuouslybetween a reaction zone and a regeneration zone and acts as a vehicle totransfer heat from the regenerator to the hydrocarbon feed and reactor.The FCC process is valuable to convert heavy hydrocarbons into morevaluable gasoline and lighter products.

The prior art, as shown in FIG. 1, uses an open reactor configuration inwhich catalyst particles and hydrocarbon feed, which together pass as acomingled mixture through a riser 3, enter a riser cyclone 5 via conduit17, with the catalyst being separated in the cyclone 5 from a suspensionof hydrocarbon vapor/catalyst particles and sent to the bottom of areactor vessel 1. The hydrocarbons separated in cyclone 5 pass overheadinto the reactor 1 vessel space, and from there through a second set ofcyclones 7,9 which further remove catalysts entrained in the gassuspension. In this system, any hydrocarbons exiting overhead from theriser cyclone 5 to the reactor vessel tended to remain in the reactorvessel for too long, causing overcracking and loss of control of thecracked products.

The present invention is directed to a closed reactor method andapparatus, in which catalyst particles remaining in the gas suspensionexiting overhead from the riser cyclone 5 are directly fed intosubsequent cyclones 7,9 for quick removal of the catalysts, so that thehydrocarbons may be stripped away from the catalyst and exit the reactorvessel through conduit 11 before they have time to overcrack. Thisovercracking is presently a problem because of recently developedcatalysts which have very high reactivity as opposed to earliercatalysts. Thus, in the invention, a direct conduit 19 (FIG. 2) connectsthe riser cyclone to the first of any subsequent series connectedcyclones which may be located within the FCC reactor.

It is advantageous to mix a catalyst stripping gas from the reactorvessel with the gas suspension which exits overhead from the risercyclone 5 as an aid in removing hydrocarbons from the catalystmaterials. To achieve this, the direct conduit 19 has an opening formedto admit stripper gas therein. The opening is formed by making theconduit in at least two parts. The first part is a gas extension tube 21which extends vertically from the overhead of the riser cyclone 5, andthe second is an inlet duct 23 for a next-in-line primary cyclone 7. Theinlet duct has a larger diameter than the gas extension tube so a firstannular port is formed between the two parts, and stripping gas passesthrough the annular port.

To maintain the seal required for a closed cyclone system, because thepressure in the riser cyclone 5 is higher than that of the reactorvessel 1, a sealing means is provided for an opening at a bottom of theriser cyclone 5 dipleg 29.

The invention will now be described in greater detail in connection withspecific embodiments thereof illustrated in FIGS. 2-8A. Theseembodiments, however, are not to be construed as a limitation on thescope of the invention, but are merely provided by way of exemplaryillustration.

Referring to FIG. 2, the reactor vessel 1 is provided with aconventional catalyst stripping section 49 in a lower bottom portion ofthe vessel. The reactor vessel 1 surrounds the upper terminal end of ariser 3 (also referred to as a riser conversion zone), to which areattached a riser cyclone 5, a primary cyclone 7, and secondary cyclone9. The riser cyclone 5 is attached to the riser 3 by means of a risercircuit 17, which is an enclosed conduit. The riser cyclone 5 in turn isconnected to the primary cyclone 7 by means of the riser cycloneoverhead conduit 19. The primary cyclone 7 is attached to the secondarycyclone 9 by a conventional enclosed conduit 25. Overhead gas from thesecondary cyclone 9, or other secondary cyclones in parallel (notshown), exits the reactor vessel 1 by means of an overhead conduit 11for cyclone 9, or conduit 13, for a parallel set of cyclones. The gaseswhich exit the reactor through the overhead conduit 11, and the overheadconduit 13, are combined and exit through the reactor overhead port 15.Catalyst particles separated from a suspension of hydrocarbon vapor andcatalyst particles by the cyclones 5,7,9 drop through cyclone diplegs29, 31, and 33 respectively and feed the reactor stripper zone 49, whichremoves hydrocarbons adhering to said catalyst. It will be apparent tothose skilled in the art that although only one series connection ofcyclones 5,7,9 are shown in the embodiment of FIG. 2, more than oneseries connection and/or more or less than three consecutive cyclones ina series connection could be used.

The riser cyclone overhead conduit 19 provides a passageway forcatalysts to directly travel from the riser cyclone 5 to the primarycyclone 7 without entering the reactor vessel 1 atmosphere. However, anannular port 27 (FIGS. 4, 5, 7, 7A, 8, 8A) is provided to admitstripping gas from the reactor vessel 1 into the conduit 19 to aid inseparating catalyst from hydrocarbons adhering thereto. As illustratedby FIG. 4, the conduit 19 comprises two parts, a gas tube extension 21and an inlet duct 23 of the primary cyclone 7. The inlet duct 23 is ofgreater diameter than the gas tube extension 21. As a consequence,annular port 27 is formed when the ends of the gas tube extension 21 andinlet duct 23 overlap. FIG. 5 shows in detail a top view of the gas tubeextension 21, concentric with the inlet duct 23 of the primary cyclone7. As shown in FIG. 4, the annular port may be located in a verticalportion of the conduit 19, but the annular port could also be located ina horizontal portion 24. The annular port should be dimensioned to havean area which allows the stripping gas to pass through the annular portat a velocity between 5-100 feet per second.

The principal purpose of conduits 17, 19, 25 and 11 is to provide adirect passage of the cracked hydrocarbons from the riser 3 to andthrough the riser cyclone 5, the primary cyclone 7, and the secondarycyclone 9, which limits the time the cracked hydrocarbons are exposed toelevated cracking temperatures. Otherwise, the cracked hydrocarbons, asin the FIG. 1 prior art apparatus, would pass randomly through the upperportion of the reactor vessel 1 to the cyclone separators which wouldprovide additional opportunity for non-selective thermal cracking of thehydrocarbons and a lowering of the product yield. Thus, with theinvention, the hydrocarbons can be quenched and fractionated in acontrolled manner in the main fractionator (downstream of overhead port15) of the processing unit, thereby limiting undesirable thermalovercracking. With the invention, the separation of catalyst fromcarbonaceous materials is achieved efficiently, while at the same time,the length of time that the gaseous materials are subjected to highcracking reaction temperatures after separation from the catalyst isminimized.

The separated catalyst from cyclones 5, 7 and 9 pass through respectivediplegs 29, 31 and 33 and are discharged therefrom after a suitablepressure is generated within the diplegs by the buildup of the catalyst.The catalyst falls from the diplegs into a bed of catalyst 51therebelow. Within catalyst bed 51 is a conventional stripping section49, where the catalyst in bed 51 is contacted with a stream of gas suchas steam, flowing countercurrently to the direction of flow of thecatalyst. The gas is introduced into the lower portion of the strippingsection 49 by one or more conventional conduits 55. Stripped catalyst isremoved by a conduit 57 for passage to either a catalyst regenerationzone or a second stage of hydrocarbon conversion zone, depending on theactivity and the amount of carbonaceous material, e.g., coke, depositedon the catalyst particles.

In the method and apparatus of the present invention, the pressureinside the riser cyclone 5 is slightly higher than the pressuresurrounding it, therefore a seal is required on the riser cyclone dipleg29 to preserve the principle of the closed cyclone system. The seal maybe provided by extending the dipleg 29 into the catalyst bed 51, thuscausing catalyst to build up around the dipleg to a selected heightdepending on the pressure imposed on the system. The seal of catalystaround the dipleg substantially prevents the flow of gaseous materialinto the dipleg. If desired, steam may be injected through a steam line43 into the riser cyclone dipleg 29 to further aid in separating thehydrocarbon vapors from catalyst particles entering the cyclone.

In another embodiment of the invention, shown as FIGS. 3 and 6, theriser cyclone 5 may be modified to incorporate a seal pot 35, ratherthan extending the riser cyclone dipleg 29 into the catalyst bed 51.FIG. 6 illustrates that the seal pot 35 comprises side walls 37, aconical bin 39 attached to side walls 37, and a drain hole 41 attachedat the base of the bin 39. The side walls 37 of the seal pot 35 have alarger diameter than that of the riser cyclone dipleg 29, thus formingan annular port 53 for catalyst to flow through. The drain hole 41 maybe concentric with the seal pot 35 and is sized such that some catalystoverflows the pot through the annular port 53, thus providing a positiveseal at all catalyst flow rates. The proper sizing is a combination ofdrain hole area, annular port area, wall height and bin height. Anexemplary size for the seal, when used with a dipleg of 26 inches OD, isas follows: seal pot diameter 42 inches ID, wall height 30 inches, binangle from a horizontal plane 60°.

At shutdown, the seal pot 35 drains quickly and thus avoids coking-up ofstagnant catalyst. The seal pot 35 can be equipped with a cone-shapeddeflector 59 (FIG. 3) located beneath the drain hole 41 much like thedeflectors used for conventional cyclone diplegs. As an additionalprecaution against coking, the seal pot 35 can also be equipped with asteam ring 47 inside at the bottom of side walls 37.

Although annular port 27 inherently accomodates thermal expansion of gastube 21 and inlet duct 23, in some instances, it may be difficult toalign the gas tube 21 with inlet duct 23 to maintain the smalldimensional tolerances required for annular port 27. Therefore, to solvethis potential problem, an aligning mechanism may be provided in theannular port 27, as shown in FIGS. 7, 7A, 8 and 8A. The aligningmechanism may comprise a packing 61 which partially fills the annularport 27, or mechanical spacers 63 which interconnect the gas tube 21 andinlet duct 23 and partially fill the annular port 27.

In the method of the invention, hydrocarbons and catalyst particles areintroduced by feeder 6 to the upstream end of a riser 3 so that acracked hydrocarbon exits the downstream (upper) end of the riser 3,which terminates within a reactor vessel 1. The cracked hydrocarbon andcatalyst particle suspension then passes through a first conduit 17 to ariser cyclone 5, which separates catalyst particles from the suspension.The first conduit 17 is enclosed so that no stripping gas from thereactor vessel 1 enters therein. The suspension then passes through asecond conduit 19, which comprises a gas tube 21 and a primary cycloneinlet duct 23. The gas tube 21 has a smaller diameter than the inletduct 23, enabling the gas tube to be inserted into the inlet duct sothat the suspension of cracked hydrocarbons and catalyst particlespasses directly from gas tube 21 into inlet duct 23. In addition,stripping gas from a reactor stripping zone 49 passes into the secondconduit by means of the annular port 27, which is formed where the gastube 21 is inserted into the inlet duct 23. Then, the suspension passesthrough a subsequent cyclone 7 to remove remaining catalyst, and leavesthe reactor through the secondary cyclone overhead conduit 11, whichfeeds reactor overhead port 15.

Catalyst separated from the suspension passes through cyclone diplegs29,31,33 through a dipleg sealing means and into catalyst bed 51. Thediplegs may be sealed by inserting them in the catalyst bed 51.Otherwise, the riser cyclone dipleg 29, in particular, may be sealed bya seal pot 35, which surrounds a lower opening of the dipleg 29 with abed of catalyst. The catalyst leaves the seal pot through a drain hole41 and an annular port 53, shown in FIG. 6. In addition, steam may enterthe seal pot through an optional steam ring 47, to prevent coking ofcatalyst. The other cyclone diplegs 31,33 may be sealed by conventionalmeans, such as flapper valves or by being extended into the catalyst bed51.

The invention can also be applied as a retrofit to an existing opencyclone system, thus converting the system to a closed cyclone system.The advantage of a retrofit is that it is simple and requires a minimumof expense and reactor downtime.

While specific embodiments of the method and apparatus aspects of theinvention have been shown and described, it should be apparent that manymodifications can be made thereto without departing from the spirit andscope of the invention. Accordingly, the invention is not limited by theforegoing description, but is only limited by the scope of the claimsappended hereto.

We claim:
 1. A method of fluid catalytic cracking of a hydrocarbon feedcomprising the steps of:passing a mixture, as a suspension, of saidhydrocarbon feed and a catalyst through a riser conversion zonecontained within a reactor vessel and cracking said hydrocarbon feed inthe riser conversion zone; passing the mixture from the riser conversionzone to a riser cyclone separator positioned within the reactor vesselthrough a first enclosed conduit, the first enclosed conduit completelyseparating the mixture from the atmosphere of the reactor vessel;separating at least a portion of the catalyst from the mixture in theriser cyclone separation means; passing a gaseous effluent from theriser cyclone separator to a primary cyclone separator positioned withinthe reactor vessel through a second conduit; passing the separatedcatalyst to a catalyst stripping zone positioned within the reactorvessel, said stripping zone using a stripping gas to remove hydrocarbonsentrained with the separated catalyst; passing at least a portion of astripping gas from the catalyst stripping zone directly into a firstannular port in the second conduit; passing the cracked hydrocarbons, asan effluent from said primary cyclone separator, to a downstreamfractionation apparatus; and passing the separated catalyst from saidstripping zone to a regeneration vessel.
 2. A method of claim 1, whereinsaid second conduit includes a first conduit portion and a secondconduit portion having a larger diameter than the first conduit portionand being spaced therefrom, the spacing between said first and secondconduit portions defining said annular port.
 3. A method of claim 2,wherein said first portion of said second conduit is inserted into thesecond portion of said second conduit.
 4. A method of claim 2, whereinsaid first and second conduit portions are vertically arranged.
 5. Amethod as in claim 1, wherein said stripping gas enters said firstannular port at a velocity of from about 5 to about 100 feet per second.6. A method of claim 1, further comprising the steps of passing thecatalyst removed from the mixture by the riser cyclone separator througha dipleg of said riser cyclone separator to a cyclone dipleg seal whichholds catalyst so that it surrounds a dipleg opening, said dipleg sealcomprising vertical side walls, a portion of which overlap a portion ofsaid riser cyclone separator dipleg to form a second annular portlocated above the opening of said riser cyclone separator dipleg, and abin comprising slanted walls attached to the lower edge of the sidewalls, the bin having at least one opening at its lower end.
 7. A methodof claim 6, further comprising the step of overflowing some catalystthrough the second annular port.
 8. A method of fluid catalytic crackingof a hydrocarbon feed comprising the steps of:passing a mixture, as asuspension, of said hydrocarbon feed and a catalyst through a riserconversion zone contained within a reactor vessel and cracking saidhydrocarbon feed in the riser conversion zone; passing the mixture fromthe riser conversion zone to a riser cyclone separator positioned withinthe reactor vessel through a first enclosed conduit, the first enclosedconduit completely separating the mixture from the atmosphere of thereactor vessel; separating at least a portion of the catalyst from themixture in the riser cyclone separator; passing a gaseous effluent fromthe riser cyclone separator to a primary cyclone separator positionedwithin the reactor vessel through a second conduit; passing theseparated catalyst to a catalyst stripping zone positioned within thereactor vessel, said stripping zone using a stripping gas to removehydrocarbons entrained with the separated catalyst; passing the catalystremoved from the mixture, by the riser cyclone separator, through adipleg of said riser cyclone separator to a cyclone dipleg seal whichholds catalyst so that it surrounds a dipleg opening, said dipleg sealcomprising vertical side walls, a portion of which overlaps a portion ofsaid riser cyclone separator dipleg to form an annular port locatedabove the opening of said riser cyclone separator dipleg, and a bincomprising slanted walls attached to the lower edge of the side walls,the bin having at least one opening at its lower end; passing thecracked hydrocarbons, as an effluent from said primary cycloneseparator, to a downstream fractionation apparatus; and passing theseparated catalyst from said stripping zone to a regeneration vessel. 9.A method of claim 8, further comprising the step of overflowing somecatalyst through the said annular port.